Stationary reciprocating engines operating on natural gas or other gaseous fuels use energy for ignition from a spark or from a small pilot quantity (typically five percent of the total fuel) of a liquid fuel having an adequate cetane number (typically diesel fuel oil) injected directly into the combustion chamber. The pilot ignited engines serve the major industrial markets since they exceed the spark ignited engines in durability and rating capability and offer convertibility to and from full diesel fueling while in operation. These pilot ignited engines are referred to as "gas diesel" or "dual fuel" engines.
Typical dual fuel engines are evidenced by U.S. Pat. Nos. 4,603,674 to Tamaka; 4,463,734 to Akeroyd; and 4,527,516 to Foster.
Control of engine emissions, particularly NO emissions, has become a concern as evidenced by U.S. Pat. Nos. 4,306,526 to Schaub et al; 4,524,730 to Doell et al; and my own patent 4,966,103, jointly held with Jesse G. Smith, and assigned to the assignor of the present invention, which provided an auto-ignition chamber or torch cell for dual fuel engines in the pilot oil mode. This system improved the exhaust emissions by provision of an externally disposed fluid fuel torch cell assembly that is in communication with the main piston chamber, such a cell providing means for optimum ignition of the main chamber fuel lean gaseous fuel mixture at the time of maximum efficiency near the top of the compression stroke. It is, however, primarily a dual fuel engine.